The total fossil fuel waste, and the attendant economic loss, in connection with heavy-duty diesel engine idling in the trucking industry is staggering. The adverse effects of heavy-duty diesel engine idling are pervasive. Obviously, there is the cost of diesel fuel, but in addition, low rpm (e.g. 1,000 rpm or less) idling increases maintenance costs by operating the engine under less than optimal and relatively inefficient operating conditions. Idling requires more frequent oil changes due to oil contamination and increases engine wear.
A large or heavy-duty diesel engine will typically burn at least about one gallon of diesel fuel per hour while idling. The exact cost of the related maintenance and wear and tear on the truck engine while idling is complex to calculate and certainly very dependent upon the assumptions made in the calculation. Whatever the exact cost may total, it is estimated that six of every fourteen hours of truck operation are spent idling. Diesel trucks are often left idling for hours, for example, to power cab and sleeper air-conditioning units (HVAC) and to maintain an elevated temperature in the diesel engine block in cold climates. Large diesel engines are notoriously hard to start in cold climates once the block has been allowed to cool to ambient conditions. In fact, it is suspected that many truck drivers idle their engines even more than the trucking companies realize or the industry statistics indicate.
One approach to solving heavy-duty diesel engine idling waste has been for trucking companies to establish policies requiring engine shut-down after a predetermined amount of idling. The obvious problem with this approach is that the drivers may not follow the prescribed policy. More recently, federal regulations have been enacted which will require new diesel engines to include controllers which shut down engine operation after, for example, 5 to 10 minutes of idling. This solution also can be defeated by driver modifications to the engine controllers and/or periodic engine racing. Moreover, it will be many years before such regulations will be implemented in a majority of the trucks which are on the road. Additionally, even if diesel engines are automatically shut down, all the problems with sleeper and cab air-conditioning, as well as cold weather starting will remain.
Another approach which has been taken to the problem of heavy-duty diesel engine idling has been to provide an auxiliary engine or power unit that is used to operate the truck HVAC and to maintain the engine block temperature, for example, by circulating oil and/or water from the auxiliary power unit through the main engine block. One such system is commercially distributed under the trademark PONY PACK and is described in more detail in U.S. Pat. Nos. 4,682,649 and 4,756,359. Similar truck auxiliary power systems are also disclosed in U.S. Pat. Nos. 4,448,157, 4,531,379 and 4,611,466. In these systems, the HVAC support and engine block temperature are maintained by the auxiliary engine, which burns fuel at a much lower rate, for example, one quart per hour, as opposed to one gallon per hour. The auxiliary engine oil and/or water coolant systems are connected to the main diesel engine for the circulation of coolant and lubricant at elevated temperatures to the main diesel engine. The auxiliary power unit also powers the truck's electrical system.
While constituting a significant step forward, such prior art auxiliary power systems only partially alleviate one of the major problems in connection with heavy-duty diesel engines, namely, starting. Typically, a heavy-duty diesel engine will carry a battery pack comprised of four relatively large, lead-acid batteries that are used to crank an electric starter motor in order to start the diesel engine. Under cold conditions, starting can be very difficult and even impossible. The prior art auxiliary power systems which maintain the diesel engine block temperature at an elevated level, as compared to ambient conditions, help reduce the starting problem, but they do not eliminate it. Moreover, the auxiliary power unit adds to the overall truck weight and poses a problem in terms of finding a location on the truck cab at which the auxiliary power unit can be mounted, plumbed to the main engine and safely coupled to the exhaust assembly.
It is also well known in connection with heavy-duty diesel engines that various starting techniques can be employed. The vast majority of the trucking industry employs electrical starters driven by large lead-acid battery packs. There are truck fleets, however, which also employ air starters, but most typically these systems are used in terminal-to-terminal applications because the truck will typically carry only enough compressed air for one or two starting sequences. When a trucking fleet is run from one terminal to another, both terminals will have air compressor facilities which can be used to start the diesel engines. In many longhaul applications, facilities for air starting are not as readily available, and electrical starters are usually employed.
In the shipping industry, it is known to employ auxiliary power units to allow recharging of pressure vessels carried by the ships and used for air starting of the main engines of the ship. U.S. Pat. No. 1,618,335, for example, discloses such an auxiliary powered shipboard installation in which there are a multiplicity of air accumulators and the necessary valving to operate various systems on the main engine, including an air starter, from these air accumulators. Recharging of the air accumulators can be accomplished by either the main or auxiliary engine. In the shipping industry, however, space requirements are not critical, and the system of U.S. Pat. No. 1,618,335, for example, includes six pressure vessels in the accumulator, plus a large low pressure air storage tank.
Other examples of air starting apparatus for diesel engines can be found in U.S. Pat. Nos. 2,906,088, 3,744,602 and 4,248,190.
It is also known to employ mechanical or hydraulic clutches between auxiliary power engines and main diesel engines, which are used alone or in combination with engine block heating, to start the main diesel engine. For example, U.S. Pat. Nos. 2,557,933, 2,696,203, 2,766,749, 2,943,617, 3,156,229, 3,662,544 and 4,542,722 are directed to mechanical or hydraulically coupled auxiliary and main diesel engines.
Thus, the attempts to reduce heavy-duty diesel engine idling waste have been largely directed to solving the problem by coupling an auxiliary power unit to the main engine to augment main engine heating while using the existing or original starting equipment. The result tends to be the addition of weight and volume (the auxiliary power unit), which must be carried when the engine is driving the vehicle, and little has been done to address a major source of environmental problems in the vast majority of the heavy-duty diesel engines in use today, namely, the extensive use of heavy and environmentally polluting lead-acid batteries.
Accordingly, it is an object of the present invention to provide a compact auxiliary power system for heavy-duty diesel engines and a method which will enable the realization of substantial fuel savings during idling without significant weight or volume increase which reduces running efficiency.
Another object of the present invention is to provide a compact auxiliary power system and method which can be retrofit to existing heavy-duty diesel engines to effect substantial fuel savings and to significantly reduce the negative environmental impact of lead-acid batteries which are typically used to start such engines.
A further object of the present invention is to provide an auxiliary power system for use with heavy-duty diesel engines which is inexpensive to retrofit to existing engines, which can be installed in the place of a conventional engine starter battery pack without the use of significant additional space, which is durable and reliable in its operation, and which has less adverse environmental impact than a conventional heavy-duty diesel engine.